My copending patent application, Ser. No. 725,972, filed on Apr. 22, 1985, discloses an air system for cooling a piston engine. The disclosed system includes a fan mechanism driven by a supercharger turbine to provide a source of coolant air for the engine. The present invention relates to a variation or improvement on the system described in the copending patent application.
In the present invention, the fan mechanism is driven by an auxiliary turbine located downstream from the main turbine wheel in the supercharger. Part of the airstream generated by the fan is diverted from the mainstream into an annular collector chamber that surrounds the main passageway leading to the compressor wheel in the supercharger.
The present invention differs from the invention disclosed in my copending patent application in that the fan mechanism is driven by an auxiliary turbine. Also, in the present invention I contemplate that the collected air can be used for engine cooling or for purposes other than engine cooling, e.g., cooling compressed air going to the engine, and/or cooling the engine lubricating oil, and/or providing a source of ventilation air for the crew compartment.
By using an auxiliary turbine to drive the fan, it should be possible to maintain optimum performance of the main turbine and compressor over a wide operating range (because the main turbine is required to drive only the engine charge air compressor). The addition of the second auxiliary turbine results in turbine energy available for the second stage compressor which more closely matches the engine's needs. The new system is a true two stage system with better overall range and pressure ratio capability than the single stage it replaces. The second stage turbine makes use of energy normally wasted in a conventional system. The auxiliary fan represents a relatively light load that can be adequately handled by the auxiliary turbine.